1. Field of the Invention
The present invention relates to an optical recording medium, and particularly to an optical recording medium formed of a chalcogenide oxide that may be recorded and erased by light, preferably, formed of a tellurium oxide, and a method for producing the same. More specifically, the invention relates to an optical recording medium whose optical recording properties are retained in a stabilized condition for a long period of time and which has excellent adhesive properties relative to a substrate.
2. Description of the Prior Art
For the optical recording medium, there are known a system for forming small holes or bubbles by the heat energy of a laser beam and a system for varying the optical characteristics of a film. In the former system, since a change of uneven shape occurs in a recording film layer during the recording, the recording film and the substrate are liable to change in quality and produce corrosion with the passage of time, and therefore, usually two recording media are formed into an air sandwiched construction for use. In the latter, however, such construction is not necessary and two recording media can be simply bonded together for use, and therefore, this system has an advantage in that the manufacturing step may be simplified considerably. Among materials used for the latter system, there is known a material having high sensitivity, that is, a material whose optical characteristics are greatly changed with respect to a predetermined incident light intensity, such as a chalcogenide oxide, particularly, a tellurium oxide TeOx, where x is 0&lt;x&lt;2.0.
Known methods for producing a tellurium oxide film include a method which comprises placing a powder of TeO.sub.2 on a boat-type heater of W or Mo, heating the heater, and effecting vacuum evaporation while reducing part of the TeO.sub.2 ; a method which comprises introducing a mixture of TeO.sub.2 powder and various reduced metals into a quartz crucible under vacuum, and a method which comprises using individual vaporizing sources to simultaneously vaporize TeO.sub.2 and metal Te.
Among these methods, the former two methods are simple but in these two methods, the boat or reducing force of the reducing metal changes during the evaporation, and therfore these methods have a disadvantage in that the composition of the vaporized film in the wall-thickness direction is subjected to an irregular change.
According to the method which uses two vaporizing sources, an even film can be obtained. The film of TeOx produced by this method wherein x is less than 1 has the advantages in that the blackening initiation temperature is low and the sensitivity is high. However, where the film is left under a relatively high temperature which is less than the blackening initiation temperature and where it is left under a high humidity, the change of transmittance is great. For this reason, TeOx which is poor in sensitivity but wherein x is more than 1 is generally used mainly in view of stability of the film. Where for the substrate, plastics materials such as an acrylic sheet, a polycarbonate sheet etc. are used, these materials are relatively large in gas transmission rate, therefore posing a problem in that vapor, oxygen and the like enter with the passing of time to oxidize the chalcogenide suboxide, thus reducing the sensitivity.
Many techniques intended to improve the stability of the chalcogenide group recording media have already been disclosed, for example, such as scattering into metal having good corrosion-resistance (Japanese Patent Application Laid-Open No. 164,037/83), coating with an organic material (Japanese Patent Application Laid-Open Nos. 21,892/81, 125,248/83 and 203,643/83); coating with an inorganic material Japanese Patent Application Laid-Open No. 199,449/83); forcible oxididation of a surface (Japanese Patent Application Laid-Open Nos. 3,442/81, 94,144/83, 189,850/83 and 2,245/84), which often involve cumbersome operation, and insufficient effect).